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Consolidated Balance Sheets (Parenthetical) - USD ($)
Dec. 31, 2015
Dec. 31, 2014
Allowance for doubtful accounts $ 596,380 $ 544,932
Preferred stock, par value $ 0.001 $ 0.001
Preferred stock, shares authorized 10,000,000 10,000,000
Preferred stock, shares issued 0 0
Treasury stock, Class A common stock shares 2,882,179 2,830,904
Class A Common Stock [Member]    
Common stock, par value $ 0.001 $ 0.001
Common stock, shares authorized 150,000,000 150,000,000
Common stock, shares issued 9,449,956 9,275,746
Common stock, shares outstanding 6,567,777 6,444,842
Class B Common Stock [Member]    
Common stock, par value $ 0.001 $ 0.001
Common stock, shares authorized 75,000,000 75,000,000
Common stock, shares issued 16,662,743 16,662,743
Common stock, shares outstanding 16,662,743 16,662,743